Age Isn't A Number
by Revaliciousness
Summary: A first year hits Kirishima with a de-aging quirk on accident and class 1A is given the task of babysitting him


**Day One**

The kid standing next to Kirishima looked a thousand times more frazzled than the boy who he'd affected with his quirk. It was always something Aizawa admired about the peppy redhead, he was tough to get down, and if another person's feelings were involved he was all the stronger.

"I'm so, so sorry, sempai, I really am! I didn't mean to, but I've never been good at controlling my quirk! I wouldn't blame you if you hated me forever!"

"Whoa there, dude!" Kirishima's arms were waving in the air, trying to get the kid one year his younger not to burst into tears and make more of a scene than he already was, "Seriously it's okay! It was an accident, just tell me how long this is supposed to last for?"

Recovery Girl was doing a quick check of his vitals while Aizawa hovered in the doorway, waiting to hear what nonsense had befallen his student by the hands of a first year.

"I've never seen it go more than a week," the kid rubbed his eyes and swallowed.

"Damn, I might miss some school," Kirishima gave a frowny pout and then quickly perked up a smile when he saw the kid turn scared again, "It won't hurt will it?"

He shook his head. "I don't think so, but you'll de-age over the next couple days and then age back. I wish it wore off quicker but…"

"It'll be fine," Aizawa sighed thoughtfully, "You can just do his work for him in the meantime."

The young eyes of the boy shot up in horror. "But I'm just a first year I don't even know-"

"Consider it punishment for being so careless and an alternative to me recommending having you expelled."

Kirishima gave a comforting pat on the boy's shoulder, but didn't argue.

The boy would take over Kirishima's work and the rest of the week would be focused on handling the effects of the boy's strange quirk.

Aizawa remembered the kid's quirk from his admissions file. It was an aging quirk, reversing or accelerating a person's age for a short period of time before it boomeranged back to normal. From what the boy had said, it sounded like it was going to work in the reverse fashion and there was no telling how young Kirishima would be before coming back to his right age.

A problem, no doubt, but perhaps there was an educational opportunity here...and he knew just how he would do that.

**Day Two**

"He's so...short…"

"Be nice...he's just younger is all."

"The real question is, has this change affected his quirk?"

Kirishima nervously grit teeth, looking up at his classmates who were once his same age, with a wary grip on his own arm.

"I'm standing right here…" Kirishima grumbled under his breath, quietly so that he was almost impossible to hear.

The trio in front of him looked as out of place as he seemed to feel. Overnight Kirishima had reversed back to the overall maturity of a twelve year old and his size had considerably shrunken. But it was his shy attitude and refusal to look his friends in the eye that stood out despite it.

Aizawa had assigned "babysitters" for the next few days to look after him, which was what had gathered the seemingly unqualified group of Todoroki, Tokoyami, and Yaomomo. It didn't make sense to him or to the three teenagers put in charge of him, but Aizawa wasn't listening to complaints.

Yaomomo made sense because she had a leaderly yet nurturing heir. But Todoroki was not known for being personable. And Tokoyami, was frankly a little scary to the now preteen.

"Sorry, Kirishima," Momo rubbed her neck, seeing how rude they'd sounded.

"Are you still able to remember everything or has your memory reversed too?" Tokoyami asked thoughtfully, Dark Shadow peeking over his shoulder, eyeing Kirishima curiously.

"I remember most things," Kirishima squeezed his arm, "I just...feel like a little kid again."

The red haired boy sighed and fell back onto his chair, propping his chin on his lifted knees. Tokoyami and Dark Shadow staring like he was a science project as Momo shifted nervously, and Todoroki eyed the ground in total confusion.

"How so?" Momo asked.

Kirishima shrugged. "Just...kinda...uncomfortable...small...it's stupid, I don't know."

"Were you shy or insecure as a preteen?" Todoroki chose then to speak and Momo looked at him like he'd dropped an entire cake on someone's birthday.

"You can't just ask people that!" Momo fussed.

"It's okay, Yaomomo," Kirishima rushed to assure them, a tiny spark of his true self slipping through, "I just don't really want to talk about it."

"An unfortunate cycle, to overcome then be returned to your tormented years."

"Tokoyami don't say stuff like that!" Momo looked about to pull her hair out.

"Perhaps it won't be as bad this time," Todoroki suggested, "Maybe we can help him not feel insecure this time."

"An admirable idea," Tokoyami nodded, "We could do something heroic…"

"Something manly," Todoroki concured.

Momo grabbed them both by the arms, wide eyed, this time with excitement instead of frazzled confusion. Both boys winced at how hard she gripped, the thrill clear in her expression.

"Or…" she gasped, "We could get your mind off of this horrible ordeal...Wait! I have just the thing!"

Kirishima only had enough time to unfurl from his nervous position, before he was swept away by Yaomomo, somehow managing to drag all three boys with her as she prattled excitedly about the day she was planning.

The next hour found the trio of disenchanted boys at the mall with Momo at the helm, powering through. This didn't seem like "just the thing". But Momo would hear no complaints, she just swept the group of confused boys along with her into the nearest suit store.

Momo picked out a red and black suit for Kirishima to try on and when he stepped out of the dressing room looking truly dapper, the boy smiled at his reflection in the mirror. Even Todoroki was giving it consideration, especially with how Kirishima beamed.

But then the grin faded.

"What's wrong?"

Kirishima sighed and his shoulders slumped. "I"m so small now. This suit looks good...but I...I don't think I want to stay here any longer."

He changed back into street clothes and a crestfallen Momo tried to lead them out, but it was Tokoyami to stop them this time. "Wait. It's my turn."

Confused, but intrigued, they followed Tokoyami into a dark shop. The walls were covered in band posters and overflowing graphic tees. Studded belts, eyeliner, chokers, and every other goth/punk thing in between. They hesitated at the door, but it was too much of a marvel to see Tokoyami get so excited so Momo let him do his thing. He took little Kirishima into the shop and threw a hoodie and studded belt on him, pointed at a chain wallet and seemed to find an unnatural enjoyment with selecting styles for the kid, Dark Shadow inputting here and there.

Momo could tell Kirishima was more or less uncomfortable, but saw him eyeing the hero merch side of the store as Tokoyami led him around. Again it was decided that this activity was not for him and it was Todoroki's turn to make a suggestion.

Which landed them in the cafeteria, getting soba and tea. Nothing like a snack break, but Kirishima still seemed down in the mouth.

"Have you had a good day?" Momo asked him.

He frowned into his soba with big doey red eyes. "I mean...thank you for trying to cheer me up, but...I don't know…"

"No accounting for taste," Tokoyami hummed.

"Can we go home?" Kirishima pouted.

They stood to go, but Momo stopped, determined. "Not until we make you happy," she demanded, "If we can't brighten our fellow heroes day than can we even call ourselves heroes?"

"Seriously Yaomomo, it's okay," Kirishima pled, but she didn't listen. She took the boys hands and sped away, letting the others slowly catch up to them at the biggest, brightest shop in the entire mall, a virtual wonderland of hero merchandise.

"But it's...so expensive…" Kirishima tried to complain, but she pushed him in.

"Go crazy," she smiled, "I'll take care of it."

That day Kirishima walked out of the mall on cloud nine, hugging a Crimson Riot plushy and a limited edition figurine. The babysitters grinned at the completely wonderstruck excitement of the boy, making the figurine fly through the air and rescue imaginary citizens.

He may have felt the weight of being a preteen again, but he'd also gotten the blessing of recapturing the magic.

**Day Three**

"I can't take it anymore!" Kaminari shoved his head under a pillow.

"Hey, hey, hey, hey, hey…" with every "hey" came a poke to his side.

Taking care of an eight year old Kirishima had started off fun, but the teens were not prepared for how tiring his energy would get.

Mina tried to step in to save Kaminari from the poking assault of the curious, red haired child by pulling his attention to her with the figurine he'd brought home the day before.

"Hey, Kirishima remember this? Want to go play instead of repeating silly questions?"

Kirishima pursed his lips and looked up at her. "Why are your eyes like that? Did you dye your skin pink? Does your acid taste good? Have you ever tried it? Do you think it would burn a hole in your tongue? Try it!"

"No one is eating acid," Sero moaned from the couch he'd sunk into. His arm was over his face like a dad who'd just gotten home from a long day at work.

"Do you want to play heroes and villains?" Kirishima beamed, "Kaminari can be the damsel in distress! Sero, you should tape him up!"

"No, we just played heroes and villains," Mina sighed, "Remember, you swung your stick too hard and gave Kaminari a black eye."

"Yeah, well he hit me first!" there was a whine in Kirishima's high pitched voice as he rubbed his sleeve against his nose.

"Yes and then you started fighting for real and we had to break it up," Mina eyed Kaminari with disappointment, "Come on, man."

"He started it!" Kaminari made a similar whiny sound.

Kirishima grabbed the toy out of Mina's hand and was instantly on to the next thing. He climbed onto the couch and starting jumping before he dropping on top of Kaminari, getting an "oof" from the now older boy. Mina sat back on the floor and just groaned, Sero have completely checked out and Kaminari had started to grapple with the boy in a show of pure immaturity.

"HOW DO YOU HAVE SO MUCH ENERGY?" Mina collapsed onto the ground.

"That's it," Kaminari shot up and grabbed the much smaller kid under his arms, lifting him off the couch, "It's someone else's turn!"

The other two perked up at that and followed Kaminari as he carried the scrappy child into the kitchen. There they found Hagakure, Jiro, and Asui throwing together a snack. They looked up with shock at the three frazzled teens and the child that was flying his Crimson Riot toy through the air and kicking his feet still high off the ground.

Before they could even ask what was going on, Kaminari put Kirishima down, patted his head and said. "He's your problem now!"

And like a shot they were all gone. Jiro tried to run after them and demand they take back the problem, but they were out of sight.

Kirishima was already climbing on the counter trying to catch sight of what they were cooking and Hagakure was practically gushing at how adorable his big hungry eyes were. Asui offered him a decorated cracker and his little shark teeth went at it vigorously while his legs dangled from the chair.

"Don't worry about it, Jiro," Hagakure waved her down, "He can stay with us! He's so cute! Look at his little face!"

Kirishima made a tiny angry expression.

"I'm not cute…" he said behind crumbs.

Hagakure was already squishing him and petting his red hair and gushing, doing everything in her power to prove him wrong. Asui kept the treats coming and Jiro started a game out of cleaning up that got little Kirishima excited. By the time they were done he was finally exhausted and fell asleep with his head in Hagakure's lap while they watched a show.

When Mina, Sero, and Kaminari peeked back and saw him happily sleeping the color drained from their faces. Now that just wasn't fair.

**Day Four**

When the next babysitters showed up to steal him from Hagakure, they found Kirishima was shrunken down to a toddler, drool dripping from his tiny open mouth.

Ochako was enchanted immediately and Deku was gentle in waking him up, but Bakugo approached the situation with his signature bad attitude.

"Why do we have to babysit him? Shouldn't the adults do that?"

Izuku tried to lift the half asleep boy up and found that he was too small for the dirt and crumb covered clothes his 8 year old self had been wearing the day before.

"It doesn't matter Kaachan, just go grab a t-shirt or something to put him in."

With a lot of grumbling Bakugo did as he was told, while Ochako and Izuku got him woken up. When Bakugo came back he dropped a black, skull shirt on the kid's head, which got annoyed looks from the other caretakers at his roughness. But as soon as Izuku started to try and dress him, Kirishima started crying and fussing unintelligibly, vocabulary lost in the age regression.

Both of them tried to stay gentle with Kirishima and shush him, but he was a mess of snot and tears in moments. The sound seemed to be driving Bakugo crazy and, unable to take it anymore, he shoved the other two aside and forced the shirt over the kids head, picking him up and dropping him on his hip, snapping a loud, "shut up" in his little face.

Kirishima froze big, watery eyes on him and shocked them all with a joyful laugh. Bakugo frowned at him.

"Don't laugh at me, you little shit," Bakugo yelled at the toddler in his arms.

Kirishima laughed again and grabbed tiny fingers in his fluffy hair, to Bakugo's complete chagrin. The toddler tugged, which got an "ow" from the blond and he immediately shoved the boy back to Izuku and Ochako.

"Get this brat off of me!"

The moment he was back in the gentle, loving hands of the two more responsible teens, he was a mess of tears and screams again, arms reaching pitifully back to the angry blond shirking away from him.

"I think he likes you," Izuku grinned nervously, holding him back out to Bakugo.

"I don't want him!" Bakugo stared horrified at the tear stained face.

"Please Bakugo!" Ochako pled.

With an exasperated sigh, Bakugo grabbed the kid and the crying instantly stopped. Ochako and Izuku looked between each other amazed.

Grabby little hands went back to trying to pull Bakugo's hair and the other two teens giggled at Bakugo's angry expression.

The whole day they couldn't get Kirishima away from Bakugo, he could barely put him down a minute without a crying fit. Izuku and Ochako took care of making sure he was fed, but no one else was able to hold him. Plenty of the other kids wanted a chance to snuggle the bundle of cuteness and grins, but as soon as he left Bakugo's hands he melted down.

At one point Kirishima was clinging onto his leg as Bakugo was attempting to cook lunch and pulled so hard on his pants that the teen once again lost his patience.

Bakugo grabbed the kid and held him in front of his face, rage in his eyes, hands looking like they might crush Kirishima. "I'm going to kill you when you grow up!" he shouted in his tiny face.

Ochako and Izuku were moving to intervene, not so afraid of the baby tears to save the child from being throttled. But Kirishima just giggled again and gently squeezed Bakugo's nose. The blond went very still, blinking at the big red eyes.

The other two stayed frozen, watching what would happen, waiting for him to explode. But instead Bakugo's shoulders fell with a sigh and with a half amused huff he leaned the toddler back against his shoulder, one arm under his legs as his other hand continued with cooking. He stopped fussing when Kirishima tugged his hair, just embraced the less than ideal situation, he'd been stuck with.

By nightfall Bakugo was fast asleep on the couch with a steadily smaller child snoozing on his chest. His friends didn't waste the opportunity to snap pictures of the rare moment of Bakugo with a child he wasn't trying to kill, giggling at the perfect, gentle moment.

**Day Seven**

"I'm so glad your back to normal, but I miss you being a little kid!"

"You were just the cutest thing!"

"I didn't get to hold you while you were a baby, it's not fair!"

Kirishima was so red faced he felt like a tomato. "Um...thanks guys...but…"

It didn't stop the girls from continuing their sputtering over how much they missed baby Kirishima. There were tears in a few eyes that he was all grown up again and Kirishima obviously didn't know how to deal with it. The only female face not saddened over him being grown back up was Mina who glared annoyance at him before hitting the back of his head.

"You were a pain in the ass, Kiri," she fussed and Kaminari and Sero nodded agreement over her shoulder. Which lasted only a few seconds before they had trapped him in a group hug and were bubbling over how happy they were that he was back to normal.

Todoroki and Tokoyami shouldered a crossed-armed Bakugo while the rest of the class buzzed around Kirishima and congratulated him on getting back to normal. The two found particular interest that Kirishima was still wearing the shirt Bakugo had leant him while he had been a toddler.

"You'll make a good father some day," Tokoyami mused, throwing a knowing glance to Todoroki.

"Shut up, Daffy Duck!" Bakugo snapped, indignant.

Todoroki patted the blond's shoulder, nodding agreement, "You're a natural."

"I'm gonna kill you, Icyhot!"

The two usually stoic boys shared one last nod. They saw the soft look in Bakugo's eye at their accusation of him making a good dad. He could fuss and scream all he wanted, but even he couldn't deny that it was true. And the smile Kirishima threw his way told them all that he agreed.


End file.
